Signaling for triangle mode

ABSTRACT

An apparatus for video decoding includes processing circuitry configured to receive a splitting direction syntax element, a first merge triangle index syntax element, and a second merge triangle index syntax element that are associated with a coding block of a picture. The coding block is coded according to a triangular prediction mode and partitioned into a first prediction unit and a second prediction unit according to a split direction. A first merge index identifies first motion information in a merge candidate list of the coding block. A second merge index identifies second motion information in the merge candidate list of the coding block. The coding block is reconstructed according to first prediction samples of the first prediction unit and second prediction samples of the second prediction unit. A value of the second merge triangle index syntax element is based on the first merge index.

INCORPORATION BY REFERENCE

The present application is a continuation of U.S. application Ser. No.17/118,240, filed Dec. 10, 2020, which is a continuation application ofU.S. application Ser. No. 16/425,404, filed May 29, 2019, now U.S. Pat.No. 10,893,298, which claims the benefit of priority to U.S. ProvisionalApplication No. 62/778,832, “Signaling and Derivation for TriangularPrediction Parameters” filed on Dec. 12, 2018, each of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1(920)×1080 luminance samples and associatedchrominance samples. The series of pictures can have a fixed or variablepicture rate (informally also known as frame rate), of, for example 60pictures per second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1(920)×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1 , a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The processing circuitry can beconfigured to receive a split direction syntax element, a first indexsyntax element, and a second index syntax element that are associatedwith a coding block of a picture. The coding block can be coded with atriangular prediction mode. The coding block can be partitioned into afirst triangular prediction unit and a second triangular prediction unitaccording to a split direction indicated by the split direction syntaxelement. The first and second index syntax elements can indicate a firstmerge index and a second merge index to a merge candidate listconstructed for the first and second triangular prediction units. Thesplit direction, the first merge index, and the second merge index canbe determined based on the split direction syntax element, the firstindex syntax element, and the second index syntax element. The codingblock can be reconstructed according to the determined split direction,the determined first merge index, and the determined second merge index.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows an example of candidate positions for constructing a mergecandidate list in accordance with an embodiment.

FIG. 9 shows examples of partitioning a coding unit into two triangularprediction units in accordance with an embodiment.

FIG. 10 shows an example of spatial and temporal neighboring blocks usedto construct a merge candidate list in accordance with an embodiment.

FIG. 11 shows an example of a lookup table used to derive a splitdirection and partition motion information based on a triangle partitionindex in accordance with an embodiment.

FIG. 12 shows an example of a coding unit applying a set of weightingfactors in an adaptive blending process in accordance with anembodiment.

FIG. 13 shows an example of motion vector storage in a triangularprediction mode in accordance with an embodiment.

FIGS. 14A-14D show examples of deriving bi-prediction motion vectorsbased on motion vectors of two triangular prediction units in accordancewith an embodiment.

FIG. 15 shows an example of a triangular prediction process inaccordance with some embodiments.

FIG. 16 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Coding Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4 . Brieflyreferring also to FIG. 4 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6 .

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7 .

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Triangular Prediction

1. Coding in Merge Mode

A picture can be partitioned into blocks, for example, using a treestructure based partition scheme. The resulting blocks can then beprocessed with different processing modes, such as an intra predictionmode, an inter prediction mode (e.g., merge mode, skip mode, advancedmotion vector prediction (AVMP) mode), and the like. When a currentlyprocessed block, referred to as a current block, is processed with amerge mode, a neighbor block can be selected from a spatial or temporalneighborhood of the current block. The current block can be merged withthe selected neighbor block by sharing a same set of motion data (orreferred to as motion information) from the selected neighbor block.This merge mode operation can be performed over a group of neighborblocks, such that a region of neighbor blocks can be merged together andshare a same set of motion data. During transmission from an encoder toa decoder, an index indicating the motion data of the selected neighborblock can be transmitted for the current block, instead of transmissionof the whole set of motion data. In this way, an amount of data (bits)that are used for transmission of motion information can be reduced, andcoding efficiency can be improved.

In the above example, the neighbor block, which provides the motiondata, can be selected from a set of candidate positions. The candidatepositions can be predefined with respect to the current block. Forexample, the candidate positions can include spatial candidate positionsand temporal candidate positions. Each spatial candidate position isassociated with a spatial neighbor block neighboring the current block.Each temporal candidate position is associated with a temporal neighborblock located in another coded picture (e.g., a previously codedpicture). Neighbor blocks overlapping the candidate positions (referredto as candidate blocks) are a subset of the spatial or temporal neighborblocks of the current block. In this way, the candidate blocks can beevaluated for selection of a to-be-merged block instead of the whole setof neighbor blocks.

FIG. 8 shows an example of candidate positions. From those candidatepositions, a set of merge candidates can be selected to construct amerge candidate list. For example, the candidate positions as defined inFIG. 8 can be used in the HEVC standard. As shown, a current block (810)is to be processed with merge mode. A set of candidate positions {A1,B1, B0, A0, B2, C0, C1} are defined for the merge mode processing.Specifically, candidate positions {A1, B1, B0, A0, B2} are spatialcandidate positions that represent positions of candidate blocks thatare in the same picture as the current block (810). In contrast,candidate positions {C0, C1} are temporal candidate positions thatrepresent positions of candidate blocks that are in another codedpicture and neighbor or overlap a co-located block of the current block(810). As shown, the candidate position C1 can be located near (e.g.,adjacent to) a center of the current block (810).

A candidate position can be represented by a block of samples or asample in different examples. In FIG. 8 , each candidate position isrepresented by a block of samples, for example, having a size of 4×4samples. A size of such a block of samples corresponding to a candidateposition can be equal to or smaller than a minimum allowable size of PBs(e.g., 4×4 samples) defined for a tree-based partitioning scheme usedfor generating the current block (810). Under such a configuration, ablock corresponding to a candidate position can always be covered withina single neighbor PB. In an alternative example, a sample position(e.g., a bottom-right sample within the block A1, or a top-right samplewithin the block A0) may be used to represent a candidate position. Sucha sample is referred to as a representative sample, while such aposition is referred to as a representative position.

In one example, based on the candidate positions {A1, B1, B0, A0, B2,C0, C1} defined in FIG. 8 , a merge mode process can be performed toselect merge candidates from the candidate positions {A1, B1, B0, A0,B2, C0, C1} to construct a candidate list. The candidate list can have apredefined maximum number of merge candidates, Cm. Each merge candidatein the candidate list can include a set of motion data that can be usedfor motion-compensated prediction.

The merge candidates can be listed in the candidate list according to acertain order. For example, depending on how the merge candidate isderived, different merge candidates may have different probabilities ofbeing selected. The merge candidates having higher probabilities ofbeing selected are positioned in front of the merge candidates havinglower probabilities of being selected. Based on such an order, eachmerge candidate is associated with an index (referred to as a mergeindex). In one embodiment, a merge candidate having a higher probabilityof being selected will have a smaller index value such that fewer bitsare needed for coding the respective index.

In one example, the motion data of a merge candidate can includehorizontal and vertical motion vector displacement values of one or twomotion vectors, one or two reference picture indexes associated with theone or two motion vectors, and optionally an identification of whichreference picture list is associated with each index.

In an example, according to a predefined order, a first number of mergecandidates, Ca, is derived from the spatial candidate positionsaccording to the order {A1, B1, B0, A0, B2}, and a second number ofmerge candidates, Cb=Cm−Ca, is derived from the temporal candidatepositions according to the order {C0, C1}. The numerals A1, B1, B0, A0,B2, C0, C1 for representing candidate positions can also be used torefer to merge candidates. For example, a merge candidate obtained fromcandidate position A1 is referred to as the merge candidate A1.

In some scenarios, a merge candidate at a candidate position may beunavailable. For example, a candidate block at a candidate position canbe intra-predicted, outside of a slice or tile including the currentblock (810), or not in a same coding tree block (CTB) row as the currentblock (810). In some scenarios, a merge candidate at a candidateposition may be redundant. For example, one neighbor block of thecurrent block (810) can overlap two candidate positions. The redundantmerge candidate can be removed from the candidate list (e.g., byperforming a pruning process). When a total number of available mergecandidates (with redundant candidates being removed) in the candidatelist is smaller than the maximum number of merge candidates Cm,additional merge candidates can be generated (e.g., according to apreconfigured rule) to fill the candidate list such that the candidatelist can be maintained to have a fixed length. For example, additionalmerge candidates can include combined bi-predictive candidates and zeromotion vector candidates.

After the candidate list is constructed, at an encoder, an evaluationprocess can be performed to select a merge candidate from the candidatelist. For example, rate-distortion (RD) performance corresponding toeach merge candidate can be calculated, and the one with the best RDperformance can be selected. Accordingly, a merge index associated withthe selected merge candidate can be determined for the current block(810) and signaled to a decoder.

At a decoder, the merge index of the current block (810) can bereceived. A similar candidate list construction process, as describedabove, can be performed to generate a candidate list that is the same asthe candidate list generated at the encoder side. After the candidatelist is constructed, a merge candidate can be selected from thecandidate list based on the received merge index without performing anyfurther evaluations in some examples. Motion data of the selected mergecandidate can be used for a subsequent motion-compensated prediction ofthe current block (810).

A skip mode is also introduced in some examples. For example, in theskip mode, a current block can be predicted using a merge mode asdescribed above to determine a set of motion data, however, no residueis generated, and no transform coefficients are transmitted. A skip flagcan be associated with the current block. The skip flag and a mergeindex indicating the related motion information of the current block canbe signaled to a video decoder. For example, at the beginning of a CU inan inter-picture prediction slice, a skip flag can be signaled thatimplies the following: the CU only contains one PU (2N×2N); the mergemode is used to derive the motion data; and no residual data is presentin the bitstream. At the decoder side, based on the skip flag, aprediction block can be determined based on the merge index for decodinga respective current block without adding residue information. Thus,various methods for video coding with merge mode disclosed herein can beutilized in combination with a skip mode.

2 Triangular Prediction Mode

A triangular prediction mode can be employed for inter prediction insome embodiments. In an embodiment, the triangular prediction mode isapplied to CUs that are 8×8 samples or larger in size and are coded inskip or merge mode. In an embodiment, for a CU satisfying theseconditions (8×8 samples or larger in size and coded in skip or mergemode), a CU-level flag is signaled to indicate whether the triangularprediction mode is applied or not.

When the triangular prediction mode is used, in some embodiments, a CUis split evenly into two triangle-shaped partitions, using either thediagonal split or the anti-diagonal split as shown in FIG. 9 . In FIG. 9, a first CU (910) is split from a top-left corner to a bottom-rightcorner resulting in two triangular prediction units, PU1 and PU2. Asecond CU (920) is split from a top-right corner to a bottom-left cornerresulting in two triangular prediction units, PU1 and PU2. Eachtriangular prediction unit PU1 or PU2 in the CU (910) or (920) isinter-predicted using its own motion information. In some embodiments,only uni-prediction is allowed for each triangular prediction unit.Accordingly, each triangular prediction unit has one motion vector andone reference picture index. The uni-prediction motion constraint can beapplied to ensure that, similar to a conventional bi-prediction method,not more than two motion compensated predictions are performed for eachCU. In this way, processing complexity can be reduced. Theuni-prediction motion information for each triangular prediction unitcan be derived from a uni-prediction merge candidate list. In some otherembodiments, bi-prediction is allowed for each triangular predictionunit. Accordingly, the bi-prediction motion information for eachtriangular prediction unit can be derived from a bi-prediction mergecandidate list.

In some embodiments, when a CU-level flag indicates that a current CU iscoded using the triangle partition mode, an index, referred to astriangle partition index, is further signaled. For example, the trianglepartition index can have a value in a range of [0, 39]. Using thistriangle partition index, the direction of the triangle partition(diagonal or anti-diagonal), as well as the motion information for eachof the partitions (e.g., merge indices to the respective uni-predictioncandidate list) can be obtained through a look-up table at the decoderside. After predicting each of the triangular prediction unit based onthe obtained motion information, in an embodiment, the sample valuesalong the diagonal or anti-diagonal edge of the current CU are adjustedby performing a blending process with adaptive weights. As a result ofthe blending process, a prediction signal for the whole CU can beobtained. Subsequently, a transform and quantization process can beapplied to the whole CU in a way similar to other prediction modes.Finally, a motion field of a CU predicted using the triangle partitionmode can be created, for example, by storing motion information in a setof 4×4 units partitioned from the CU. The motion field can be used, forexample, in a subsequent motion vector prediction process to construct amerge candidate list.

3. Uni-Prediction Candidate List Construction

In some embodiments, a merge candidate list for prediction of twotriangular prediction units of a coding block processed with atriangular prediction mode can be constructed based on a set of spatialand temporal neighboring blocks of the coding block. In one embodiment,the merge candidate list is a uni-prediction candidate list. Theuni-prediction candidate list includes five uni-prediction motion vectorcandidates in an embodiment. For example, the five uni-prediction motionvector candidates are derived from seven neighboring blocks includingfive spatial neighboring blocks (labelled with numbers of 1 to 5 in FIG.10 ) and two temporal co-located blocks (labelled with numbers of 6 to 7in FIG. 10 ).

In an example, the motion vectors of the seven neighboring blocks arecollected and put into the uni-prediction candidate list according tothe following order: first, the motion vectors of the uni-predictedneighboring blocks; then, for the bi-predicted neighboring blocks, theL0 motion vectors (that is, the L0 motion vector part of thebi-prediction MV), the L1 motion vectors (that is, the L1 motion vectorpart of the bi-prediction MV), and averaged motion vectors of the L0 andL1 motion vectors of the bi-prediction MVs. In an example, if the numberof candidates is less than five, zero motion vectors are added to theend of the list. In some other embodiments, the merge candidate list mayinclude less than 5 or more than 5 uni-prediction or bi-prediction mergecandidates that are selected from candidate positions that are the sameor different from that shown in FIG. 10 .

4. Lookup Table and Table Indices

In an embodiment, a CU is coded with a triangular partition mode with amerge candidate list including five candidates. Accordingly, there are40 possible ways to predict the CU when 5 merge candidates are used foreach triangular PU. In other words, there can be 40 differentcombinations of split directions and merge indices: 2 (possible splitdirections)×(5 (possible merge indices for a first triangular predictionunit)×5 (possible merge indices for a second triangular predictionunit)−5 (a number of possibilities when the pair of first and secondprediction units shares a same merge index)). For example, when a samemerge index is determined for the two triangular prediction units, theCU can be processed using a regular merge mode, for example, describedin the section of II. 1, instead of the triangular predication mode.

Accordingly, in an embodiment, a triangular partition index in the rangeof [0, 39] can be used to represent which one of the 40 combinations isused based on a lookup table. FIG. 11 shows an exemplary lookup table(1100) used to derive the split direction and merge indices based on atriangular partition index. As shown in the lookup table (1100), a firstrow (1101) includes the triangular partition indices ranging from 0 to39; a second row (1102) includes possible split directions representedby 0 or 1; a third row (1103) includes possible first merge indicescorresponding to a first triangular prediction unit and ranging from 0to 4; and, a fourth row 1104 includes possible second merge indicescorresponding to a second triangular prediction unit and ranging from 0to 4.

For example, when a triangular partition index having a value of 1 isreceived at a decoder, based on a column (1120) of the lookup table(1100), it can be determined that the split direction is a partitiondirection represented by the value of 1, and the first and second mergeindices are 0 and 1, respectively. As the triangle partition indices areassociated with a lookup table, a triangle partition index is alsoreferred to as a table index in this disclosure.

5. Adaptive Blending along the Triangular Partition Edge

In an embodiment, after predicting each triangular prediction unit usingrespective motion information, a blending process is applied to the twoprediction signals of the two triangular prediction units to derivesamples around the diagonal or anti-diagonal edge. The blending processadaptively chooses between two groups of weighting factors depending onthe motion vector difference between the two triangular predictionunits. In an embodiment, the two weighting factor groups are as follows:

(1) 1st weighting factor group: {7/8, 6/8, 4/8, 2/8, 1/8} for samples ofa luma component and {7/8, 4/8, 1/8} for samples of chroma component;and

(2) 2nd weighting factor group: {7/8, 6/8, 5/8, 4/8, 3/8, 2/8, 1/8} forsamples of a luma component and {6/8, 4/8, 2/8} for samples of a chromacomponent.

The second weighting factor group has more luma weighting factors andblends more luma samples along the partition edge.

In an embodiment, the following condition is used to select one of thetwo weighting factor groups. When reference pictures of the two trianglepartitions are different from each other, or when a motion vectordifference between the two triangle partitions is larger than athreshold (e.g., 16 luma samples), the 2nd weighting factor group isselected. Otherwise, the 1st weighting factor group is selected.

FIG. 12 shows an example of a CU applying the first weighting factorgroup. As shown, a first coding block (1201) includes luma samples, anda second coding block (1202) includes chroma samples. A set of pixelsalong a diagonal edge in the coding block (1201) or (1202) are labeledwith the numbers 1, 2, 4, 6, and 7 corresponding to the weightingfactors 7/8, 6/8, 4/8, 2/8, and 1/8, respectively. For example, for apixel labelled with the number of 2, a sample value of the pixel after ablending operation can be obtained according to:

the blended sample value=2/8×P1+6/8×P2,

where P1 and P2 represent sample values at the respective pixel butbelonging to predictions of a first triangular prediction unit and asecond triangular prediction unit, respectively.

6. Motion Vector Storage in a Motion Field

FIG. 13 shows an example of how motion vectors of two triangularprediction units in a CU coded with a triangular prediction mode arecombined and stored to form a motion field useful for subsequent motionvector prediction. As shown, a first coding block (1301) is partitionedalong a first diagonal edge (1303) into two triangular prediction unitsfrom a top-left corner to a bottom-right corner, while a second codingblock (1302) is partitioned along a second diagonal edge (1304) into twotriangular prediction units from a top-right corner to a bottom-leftcorner. A first motion vector corresponding to a first triangularprediction unit of the coding block (1301) or (1302) is represented asMv1, while a second motion vector corresponding to a second triangularprediction unit of the coding block (1301) or (1302) is represented asMv2. Taking the coding block (1301) as an example, at the decoder side,two merge indices corresponding to the first and second triangularprediction units in the coding block (1301) can be determined based onreceived syntax information. After a merge candidate list is constructedfor the coding block (1301), Mv1 and Mv2 can be determined according tothe two merge indices.

In an embodiment, the coding block (1301) is partitioned into multiplesquares having a size of 4×4 samples. Corresponding to each 4×4 square,either a uni-prediction motion vector (e.g., Mv1 or Mv2) or two motionvectors (forming bi-prediction motion information) are stored dependingon the position of a 4×4 square in the respective coding block (1301).As shown in the FIG. 13 example, a uni-prediction motion vector, eitherMv1 or Mv2, is stored in each 4×4 square that does not overlap thediagonal edge (1303) partitioning the coding block (1301). In contrast,two motion vectors are stored in each 4×4 square overlapping thediagonal edge (1303) partitioning the respective coding block (1301).For the coding block (1302), the motion vectors can be organized andstored in a way similar to the coding block (1301).

The pair of bi-prediction motion vectors stored in the 4×4 squaresoverlapping the respective diagonal edges can be derived from Mv1 andMv2 according to the following rules in an embodiment:

(1) In the case that Mv1 and Mv2 are motion vectors towards differentdirections (e.g., associated with different reference picture list L0 orL1), Mv1 and Mv2 are combined to form the pair of bi-prediction motionvectors.

(2) In the case that both Mv1 and Mv2 are towards a same direction(e.g., associated with a same reference picture list L0 (or L1)):

-   -   (2.a) When the reference picture of Mv2 is the same as a picture        in the reference picture list L1 (or L0), Mv2 is changed to be        associated with that reference picture in the reference picture        list L1 (or L0). Mv1 and Mv2 with modified associated reference        picture list are combined to form the pair of bi-prediction        motion vectors.    -   (2.b) When the reference picture of Mv1 is the same as a picture        in the reference picture list L1 (or L0), Mv1 is changed to be        associated with the reference picture in the reference picture        list L1 (L0). The Mv1 with modified associated reference picture        list and Mv2 are combined to form the pair of bi-prediction        motion vectors.    -   (2.c) Otherwise, only Mv1 is stored for the respective 4×4        square.

FIGS. 14A-14D show examples of the derivation of the pair ofbi-prediction motion vectors according to exemplary set of rules. Tworeference picture lists are used in FIGS. 14A-14D: a first referencepicture list L0 includes reference pictures with picture order count(POC) numbers of POC 0 and POC 8, and having reference picture indices(refIdx) of 0 and 1, respectively. While a second reference picture listL1 includes reference pictures with POC numbers of POC 8 and POC 16, andhaving reference picture indices of 0 and 1, respectively.

FIG. 14A corresponds to the rule (1). As shown in FIG. 14A, Mv1 isassociated with POC 0 in L0, and thus has a reference picture indexrefIdx=0, while Mv2 is associated with POC 8 in L1, and thus has areference picture index refIdx=0. As Mv1 and Mv2 are associated withdifferent reference picture lists, Mv1 and Mv2 together are used as thepair of bi-direction motion vectors.

FIG. 14B corresponds to the rule (2.a). As shown, Mv1 and Mv2 areassociated with a same reference picture list L0. Mv2 points to POC8that is also a member of L1. Accordingly, Mv2 is modified to beassociated with POC8 in L1, and the value of the respective referenceindex is changed from 1 to 0.

FIG. 14C and FIG. 14D correspond to the rules (2b) and (2c).

7. Syntax Elements for Signaling Triangular Prediction Parameters

In some embodiments, a triangular prediction unit mode is applied to CUsin skip or merge mode. A block size of the CUs cannot be smaller than8×8. For a CU coded in a skip or merge mode, a CU level flag is signaledto indicate whether the triangular prediction unit mode is applied ornot for the current CU. In an embodiment. when the triangular predictionunit mode is applied to the CU, a table index indicating the directionfor splitting the CU into two triangular prediction units and the motionvectors (or respective merge indices) of the two triangular predictionunits are signaled. The table index ranges from 0 to 39. A look-up tableis used for deriving the splitting direction and motion vectors from thetable index.

III. Signaling and Derivation of Triangular Prediction Parameters

1. Signaling Triangular Prediction Parameters

As descried above, three parameters, a split direction, a first mergeindex corresponding to a first triangular prediction unit, and a secondmerge index corresponding to a second triangular prediction unit, aregenerated when a triangular prediction mode is applied to a codingblock. As described, in some examples, the three triangular predictionparameters are signaled from an encoder side to a decoder side bysignaling a table index. Based on a lookup table (e.g., the lookup table(1100) in the FIG. 11 example), the three triangular predictionparameters can be derived using the table index received at the decoderside. However, additional memory space is required for storing thelookup table at a decoder, which may become a burden in someimplementations of the decoder. For example, the additional memory maylead to an increase in cost and power consumption of the decoder.

The present disclosure provides a solution to solve the above problem.Specifically, instead of signaling a table index and relying on a lookuptable to interpret the table index, three syntax elements are signaledfrom an encoder side to a decoder side. The three triangular predictionparameters (the split direction and two merge indices) can be derived ordetermined at the decoder side based on the three syntax elementswithout using the lookup table. The three syntax elements can besignaled in any order for the respective coding block in an embodiment.

In an embodiment, the three syntax elements include a split directionsyntax element, a first index syntax element, and a second index syntaxelement. The split direction syntax element can be used to determine thesplit direction parameter. The first and second index syntax elements incombination can be used to determine the parameters of the first andsecond merge indices. In an embodiment, an index (referred to as atriangular prediction index, in contrast to the table index) can firstbe derived based on the first and second index syntax elements and thesplit direction syntax element. The three triangular predictionparameters can subsequently be determined based on the triangularprediction index.

There are various ways for configuring or coding the three syntaxelements in order to signal information of the three triangularprediction parameters. For the split direction syntax element, in anembodiment, the split direction syntax element takes a value of 0 or 1to indicate whether the split direction is from a top-left corner to abottom-right corner or from a top-right corner to a bottom-left corner.

For the first and second index syntax elements, in an embodiment, thefirst index syntax element is configured to have a value of theparameter of the first merge index, while the second index syntaxelement is configured to have a value of the second merge index when thesecond merge index is smaller than the first merge index, and have avalue of the second merge index minus one when the second merge index isgreater than the first merge index (the second and first merge indicesare supposed to take different value as described above, so the secondand first merge indices would not equal each other).

As an example, in an embodiment, a merge candidate list has a length of5 merge candidates. Accordingly, the first index syntax element takes avalue of 0, 1, 2, 3, or 4, while the second index syntax element takes avalue of 0, 1, 2, or 3. For example, in a case that the first mergeindex parameter has a value of 2, and the second merge index parameterhas a value of 4, to signal the first and second merge indices, thefirst and second index syntax elements would have a value of 2 and 3,respectively.

In an embodiment, a coding block is located at a position havingcoordinates of (xCb, yCb) with respect to a reference point in a currentpicture, where xCb and yCb represents the horizontal and verticalcoordinates of the current coding block, respectively. In someembodiments, xCb and yCb are aligned with the horizontal and verticalcoordinates with 4×4 granularity. Accordingly, the split directionsyntax element is represented as split_dir[xCb][yCb]. The first indexsyntax element is represented as merge_triangle_idx0[xCb][yCb]. Thesecond syntax element is represented as merge_triangle_idx1[xCb][yCb].

The three syntax elements can be signaled in arbitrary orders in abitstream. For example, the three syntax elements can be signaled in oneof the following orders: 1. split_dir, merge_triangle_idx0,merge_triangle_idx1; 2. split_dir, merge_triangle_idx1,merge_triangle_idx0; 3. merge_triangle_idx0, split_dir,merge_triangle_idx1; 4. merge_triangle_idx0, merge_triangle_idx1,split_dir; 5. merge_triangle_idx1, split_dir, merge_triangle_idx0; 6.merge_triangle_idx1, merge_triangle_idx0, split_dir.

2. Deriving Triangular Prediction Parameters

2. 1 Deriving Triangular Prediction Parameters Based on Syntax Elements

In an embodiment, the three triangular prediction parameters are derivedbased on the three syntax elements received at a decoder side. Forexample, the split direction parameter can be determined according to avalue of the split direction syntax element. The first merge indexparameter can be determined to have a value of the first index syntaxelement. The second merge index parameter can be determined to have avalue of the second index syntax element when the second index syntaxelement has a value smaller than the first index syntax element. Incontrast, the second merge index parameter can be determined to have avalue of the second index syntax element value plus 1 when the secondindex syntax element has a value greater than or equal to the firstindex syntax element.

An example of pseudocode implementing the above derivation process isshown below:

m=merge_triangle_idx0[xCb][yCb];

n=merge_triangle_idx1[xCb][yCb];

n=n+(n>=m?1:0),

where m and n represent the parameters of the first and second mergeindices, respectively, and merge_triangle_idx0[xCb][yCb] andmerge_triangle_idx1[xCb][yCb] represent the first and second indexsyntax elements, respectively.

2. 2 Deriving Triangular Prediction Parameters Based on the TriangularPrediction Index Derived from Syntax Elements

In an embodiment, a triangular prediction index is first derived basedon the three syntax elements received at a decoder side. The threetriangular prediction parameters are subsequently determined based onthis triangular prediction index. For example, values of the threesyntax elements in binary bits can be combined into a bit string thatforms the triangular prediction index. Later, the bits of the respectivesyntax elements can be extracted from the bit string and used todetermine the three triangular prediction parameters.

In an embodiment, the triangular prediction index is derived as a linearfunction of the three syntax elements according to:

mergeTriangleIdx[xCb][yCb]=a*merge_triangle_idx0[xCb][yCb]+b*merge_triangle_idx1[xCb][yCb]+c*split_dir[xCb][yCb],

where mergeTriangleIdx[xCb][yCb] represents the triangular predictionindex, a, b and c are integer constants, andmerge_triangle_idx0[xCb][yCb], merge_triangle_idx1[xCb][yCb] andsplit_dir[xCb][yCb] represent the three signaled syntax elements, namelythe first index syntax element, the second index syntax element and thesplit direction syntax element, respectively.

As an example, in the above example where the merge candidate listincludes 5 merge candidates, the constants can take the followingvalues: a=8, b=2, and c=1. In this scenario, the above linear functionis equivalent to left-shifting the value of the first index syntaxelement 3 bits, left-shifting the value of the second index syntaxelement 2 bits, and then combining the bits of three syntax elementsinto a bit string by the addition operation.

In other examples, a merge candidate list may have a length differentfrom the length of 5. Accordingly, the first and second merge indexparameters may have values in a range different from [0, 4]. Therespective first and second index syntax elements may also have valuesin different ranges. The constant a, b, and c may accordingly takedifferent values in order to properly combine the three syntax elementsinto a bit string. In addition, the order of the three syntax elementsmay be arranged in a way different from the above example.

After the triangular prediction index is determined as described above,the three triangular prediction parameters can be determined based onthe determined triangular prediction index. In one embodiment,corresponding to the above example where a=8, b=2, and c=1, the splitdirection can be determined according to:

triangleDir=mergeTriangleIdx[xCb][yCb]& 1,

where triangleDir represents the split direction parameter, and the lastdigit of the triangular prediction index is extracted by the binary ANDoperation (&) to be a value of the split direction parameter.

In an embodiment, corresponding to the above example where a=8, b=2, andc=1, the first and second merge indices can be determined according tothe following pseudocode:

m=mergeTriangleIdx[xCb][yCb]>>3; //excluding the last three bits

n=(mergeTriangleIdx[xCb][yCb]>>1) & 3; //extracting the second last andthe third last bits

n=n+(n>=m?1:0).

As shown, the bits in the triangular prediction index excluding the lastthree bits are used as the first merge index parameter. The second lastand third last bits in the triangular prediction index are used as thesecond merge index parameter if a value of the second last and thirdlast bits is smaller than the first merge index value. Otherwise, thevalue of the second last and third last bits plus 1 is used as thesecond merge index parameter.

2. 3 Adaptive Configuration of Syntax Elements

In some embodiments, the first and second index syntax elements can beconfigured to represent different meanings depending on the splitdirection of a coding unit. Or, in other words, the first and secondindex syntax elements can be coded in different way depending on whichsplit direction is used to partition a coding unit. For example,corresponding to different split directions, probability distributionsof values of the two merge indices may be different due tocharacteristics of a current picture or local features in a currentpicture. Accordingly, the two index syntax elements can be adaptivelycoded according to the respective split direction to save bits used forindex syntax element coding.

For example, as shown in FIG. 9 example, the two triangular predictionunits, PU1 and PU2, are defined corresponding to the respective splitdirection in the coding blocks (910) and (920). When the first splitdirection from top-left to right-bottom is used as in the coding block(910), the first index syntax element can be used to carry a merge indexcorresponding to PU1 while the second index syntax element can be usedto carry merge index information corresponding to PU2. In contrast, whenthe second split direction from top-right to left-bottom is used as inthe coding block (920), the first index syntax element can be used tocarry a merge index corresponding to PU2 while the second index syntaxelement can be used to carry merge index information corresponding toPU1.

Corresponding to the adaptive coding of the index syntax elements at anencoder side, suitable decoding operations can be performed at a decoderside. A first example of pseudocode implementing adaptively decoding theindex syntax elements is shown below:

if (triangleDir = = 0) {  m = merge_triangle_idx0[xCb][yCb];  n =merge_triangle_idx1[xCb][yCb];  n = n + (n >= m ? 1 : 0); } else {  n =merge_triangle_idx0[xCb][yCb];  m = merge_triangle_idx1[xCb][yCb];  m =m + (m >= n ? 1 : 0); }

A second example of pseudocode implementing adaptively decoding theindex syntax elements is shown below where the triangular predictionindex is employed:

if (triangleDir = = 0) {  m = mergeTriangleIdx[xCb][yCb] >> 3;  n =(mergeTriangleIdx[xCb][yCb] >> 1) & 3;  n = n + (n >= m ? 1 : 0); } else{  n = mergeTriangleIdx[xCb][yCb] >> 3;  m =(mergeTriangleIdx[xCb][yCb] >> 1) & 3;  m = m + (m >= n ? 1 : 0); }

In the above first and second examples of the pseudocode, the splitdirection (represented as triangle Dir) can be determined directly fromthe split direction syntax element or can be determined according to thetriangular prediction index in different embodiments.

3. Entropy Coding of the Three Syntax Elements

3.1 Binarization of the Three Syntax Elements

The three syntax elements (split direction syntax element, first andsecond index syntax elements) used for signaling the three triangularprediction parameters (split direction and first and second mergeindices) can be coded with different binarization methods in variousembodiments.

In one embodiment, the first index syntax element is coded withtruncated unary coding. In another embodiment, the first index syntaxelement is coded with truncated binary coding. In one example, themaximum valid value of the first index syntax element equals 4. Inanother embodiment, a combination of a prefix and fixed lengthbinarization is used for coding the first index syntax element. In oneexample, a prefix bin is first signaled to indicate whether the firstindex syntax element is 0. When the first index syntax element is notzero, additional bins are coded with a fixed-length to indicate theactual value of the first index syntax element. Examples of truncatedunary coding, truncated binary coding, and prefix and fixed-lengthcoding with a maximum valid value equal to 4 are shown in Table 1.

TABLE 1 truncated unary truncated binary prefix + fixed- symbol codingcoding length coding 0 0 00 0 1 10 01 100 2 110 10 101 3 1110 110 110 41111 111 111

In one embodiment, the second index syntax element is coded withtruncated unary coding. In another embodiment, the second index syntaxelement is coded with binary coding (i.e., fixed length coding with 2bits). Examples of truncated unary coding and binary coding with amaximum valid value equal 3 are shown in Table 2.

TABLE 2 symbol truncated unary coding binary coding 0 0 00 1 10 01 2 11010 3 111 11

3.2 Context-Based Coding

In some embodiments, certain restrictions are applied on probabilitymodels used in the entropy coding of the three syntax elements forsignaling the three triangular prediction parameters.

In one embodiment, it is restricted to use no more than a total of Ncontext coded bins for the three syntax elements of a coding blockprocessed with a triangular prediction mode. For example, N is aninteger that can be 0, 1, 2, 3, and the like. In one embodiment, when Nis equal to 0, all bins of these three syntax elements can be coded withequal probability.

In one embodiment, when N is equal to 1, there is only one context codedbin in the group of these three syntax elements. In one example, one binin the split direction syntax element is context coded, and theremaining bins in the split direction syntax element, and all bins inthe first and second index syntax elements are coded with equalprobability. In another example, one bin in the second index syntaxelement is context coded, and the remaining bins in the second indexsyntax element, and all bins in the split direction element and thefirst index syntax element are coded with equal probability.

In one embodiment, when N is equal to 2, there are two context codedbins in the group of these three syntax elements. In one example, onebin in the first index syntax element and another bin in the secondindex syntax element are context coded, and the remaining bins of thesethree syntax elements are all coded with equal probability.

In one embodiment, when a context model is applied on a syntax element,only the first bin of the syntax element is applied with the contextmodel. The remaining bins of the syntax element are coded with equalprobability.

4. An Example Triangular Prediction Process

FIG. 15 shows a flow chart outlining a process (1500) according to anembodiment of the disclosure. The process (1500) can be used in thereconstruction of a block coded in triangular prediction mode, so as togenerate a prediction block for the block under reconstruction. Invarious embodiments, the process (1500) is executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230) and (240), the processing circuitry that performsfunctions of the video decoder (310), the processing circuitry thatperforms functions of the video decoder (410), the processing circuitrythat performs functions of the entropy decoder (771), the inter decoder(780) and the like. In some embodiments, the process (1500) isimplemented by software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1500). The process starts at (S1501) and proceeds to(S1510).

At (S1510), three syntax elements (a split direction syntax element, afirst index syntax element, and a second index syntax element) arereceived at a video decoder in a video bitstream. The three syntaxelements carry information of three triangular prediction parameters (asplit direction parameter, a first merge index parameter, and a secondmerge index parameter) of a coding block that is coded with a triangularprediction mode. For example, the coding unit is partitioned into afirst triangular predication unit and a second triangular predicationunit according to a split direction indicated by the split directionsyntax element. The first and second triangular prediction units may beassociated with the first and second merge indices, respectively, thatare associated with a merge candidate list constructed for the codingblock.

At (S1520), the three triangular prediction parameters (the splitdirection, the first merge index, and the second merge index) can bedetermined according to the three syntax elements received at (S1510).For example, various techniques described in the sections of III. 2 canbe employed to derive the three triangular prediction parameters.

At (S1530), the coding block can be reconstructed according to the splitdirection, the first merge index, and the second merge index determinedat (S1520). For example, the merge candidate list can be constructed forthe coding block. Based on the merge candidate list and the first mergeindex to the merge candidate list, a first uni-prediction motion vectorand a first reference picture index associated with the firstuni-prediction motion vector can be determined. Similarly, based on themerge candidate list and the second merge index to the merge candidatelist, a second uni-prediction motion vector and a second referencepicture index associated with the second uni-prediction motion vectorcan be determined. Subsequently, a first prediction corresponding to thefirst triangular prediction unit can be determined according to thefirst uni-prediction motion vector and the first reference picture indexassociated with the first uni-prediction motion vector. Similarly, asecond prediction corresponding to the second triangular prediction unitcan be determined according to the second uni-prediction motion vectorand the second reference picture index associated with the seconduni-prediction motion vector. Thereafter, an adaptive weighting processcan be applied to samples along a diagonal edge between the first andsecond triangular prediction units based on the first and secondpredictions to derive a final prediction of the coding block. Theprocess (1500) can proceed to (S1599), and terminates at S1599.

IV. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 16 shows a computersystem (1600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 16 for computer system (1600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1600).

Computer system (1600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1601), mouse (1602), trackpad (1603), touchscreen (1610), data-glove (not shown), joystick (1605), microphone(1606), scanner (1607), camera (1608).

Computer system (1600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1610), data-glove (not shown), or joystick (1605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1609), headphones(not depicted)), visual output devices (such as screens (1610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1620) with CD/DVD or the like media (1621), thumb-drive (1622),removable hard drive or solid state drive (1623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1600) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1649) (such as, for example USB ports of thecomputer system (1600)); others are commonly integrated into the core ofthe computer system (1600) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1600) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1640) of thecomputer system (1600).

The core (1640) can include one or more Central Processing Units (CPU)(1641), Graphics Processing Units (GPU) (1642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1643), hardware accelerators for certain tasks (1644), and so forth.These devices, along with Read-only memory (ROM) (1645), Random-accessmemory (1646), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1647), may be connectedthrough a system bus (1648). In some computer systems, the system bus(1648) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1648),or through a peripheral bus (1649). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1641), GPUs (1642), FPGAs (1643), and accelerators (1644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1645) or RAM (1646). Transitional data can be also be stored in RAM(1646), whereas permanent data can be stored for example, in theinternal mass storage (1647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1641), GPU (1642), massstorage (1647), ROM (1645), RAM (1646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1600), and specifically the core (1640) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1640) that are of non-transitorynature, such as core-internal mass storage (1647) or ROM (1645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: receiving a splitting direction syntax element, a firstmerge triangle index syntax element, and a second merge triangle indexsyntax element that are associated with a coding block of a picture, thecoding block being coded according to a triangular prediction mode andpartitioned into a first prediction unit and a second prediction unitaccording to a split direction; determining the split direction based onthe splitting direction syntax element; determining a first merge indexbased on the first merge triangle index syntax element, the first mergeindex identifying first motion information in a merge candidate list ofthe coding block; determining a second merge index based on the secondmerge triangle index syntax element, the second merge index identifyingsecond motion information in the merge candidate list of the codingblock; determining first prediction samples of the first prediction unitaccording to the first motion information; determining second predictionsamples of the second prediction unit according to the second motioninformation; and reconstructing the coding block according to the firstprediction samples of the first prediction unit and the secondprediction samples of the second prediction unit, wherein a value of thesecond merge triangle index syntax element is based on the first mergeindex.
 2. The method of claim 1, wherein the value of the second mergetriangle index syntax element is based on whether the second merge indexis less than the first merge index.
 3. The method of claim 2, whereinthe value of the second merge triangle index syntax element is equal tothe second merge index based on the second merge index being less thanthe first merge index.
 4. The method of claim 3, wherein the value ofthe second merge triangle index syntax element is equal to the secondmerge index minus 1 based on the second merge index not being less thanthe first merge index.
 5. The method of claim 1, wherein the splittingdirection syntax element is one bit.
 6. The method of claim 1, whereinthe splitting direction syntax element indicates a value that is 0 or 1.7. The method of claim 1, wherein the determining the split directioncomprises: determining the split direction is from a top-left corner toa bottom-right corner based on the splitting direction syntax elementindicating a first value; and determining the split direction is from atop-right corner to a bottom-left corner based on the splittingdirection syntax element indicating a second value.
 8. An apparatus ofvideo decoding, comprising: processing circuitry configured to: receivea splitting direction syntax element, a first merge triangle indexsyntax element, and a second merge triangle index syntax element thatare associated with a coding block of a picture, the coding block beingcoded according to a triangular prediction mode and partitioned into afirst prediction unit and a second prediction unit according to a splitdirection; determine the split direction based on the splittingdirection syntax element; determine a first merge index based on thefirst merge triangle index syntax element, the first merge indexidentifying first motion information in a merge candidate list of thecoding block; determine a second merge index based on the second mergetriangle index syntax element, the second merge index identifying secondmotion information in the merge candidate list of the coding block;determine first prediction samples of the first prediction unitaccording to the first motion information; determine second predictionsamples of the second prediction unit according to the second motioninformation; and reconstruct the coding block according to the firstprediction samples of the first prediction unit and the secondprediction samples of the second prediction unit, wherein a value of thesecond merge triangle index syntax element is based on the first mergeindex.
 9. The apparatus of claim 8, wherein the value of the secondmerge triangle index syntax element is based on whether the second mergeindex is less than the first merge index.
 10. The apparatus of claim 9,wherein the value of the second merge triangle index syntax element isequal to the second merge index based on the second merge index beingless than the first merge index.
 11. The apparatus of claim 10, whereinthe value of the second merge triangle index syntax element is equal tothe second merge index minus 1 based on the second merge index not beingless than the first merge index.
 12. The apparatus of claim 8, whereinthe splitting direction syntax element is one bit.
 13. The apparatus ofclaim 8, wherein the splitting direction syntax element indicates avalue that is 0 or
 1. 14. The apparatus of claim 8, wherein theprocessing circuitry is configured to: determine the split direction isfrom a top-left corner to a bottom-right corner based on the splittingdirection syntax element indicating a first value; and determine thesplit direction is from a top-right corner to a bottom-left corner basedon the splitting direction syntax element indicating a second value. 15.A non-transitory computer-readable medium storing instructions which,when executed by a computer for video decoding, cause the computer toperform a method of video decoding, the method comprising: receiving asplitting direction syntax element, a first merge triangle index syntaxelement, and a second merge triangle index syntax element that areassociated with a coding block of a picture, the coding block beingcoded according to a triangular prediction mode and partitioned into afirst prediction unit and a second prediction unit according to a splitdirection; determining the split direction based on the splittingdirection syntax element; determining a first merge index based on thefirst merge triangle index syntax element, the first merge indexidentifying first motion information in a merge candidate list of thecoding block; determining a second merge index based on the second mergetriangle index syntax element, the second merge index identifying secondmotion information in the merge candidate list of the coding block;determining first prediction samples of the first prediction unitaccording to the first motion information; determining second predictionsamples of the second prediction unit according to the second motioninformation; and reconstructing the coding block according to the firstprediction samples of the first prediction unit and the secondprediction samples of the second prediction unit, wherein a value of thesecond merge triangle index syntax element is based on the first mergeindex.
 16. The non-transitory computer-readable medium of claim 15,wherein the value of the second merge triangle index syntax element isbased on whether the second merge index is less than the first mergeindex.
 17. The non-transitory computer-readable medium of claim 16,wherein the value of the second merge triangle index syntax element isequal to the second merge index based on the second merge index beingless than the first merge index.
 18. The non-transitorycomputer-readable medium of claim 17, wherein the value of the secondmerge triangle index syntax element is equal to the second merge indexminus 1 based on the second merge index not being less than the firstmerge index.
 19. The non-transitory computer-readable medium of claim15, wherein the splitting direction syntax element is one bit.
 20. Thenon-transitory computer-readable medium of claim 15, wherein thesplitting direction syntax element indicates a value that is 0 or 1.